1. Field of the Invention
The present invention relates to a shutter device mounted to an image pickup apparatus, such as a digital camera, and a camera including the shutter device, and more particularly to a shutter device having a yoke which magnetically attracts an armature thereto, and a camera including the shutter device.
2. Description of the Related Art
Shutter devices mounted to image pickup apparatuses, such as a digital camera, include one having a front blade which travels to a position for opening a shutter opening at the time of exposure, and a rear blade which travels to a position for closing the shutter opening at the time of exposure.
The front blade is connected to a drive unit having a drive source, such as a spring, and an armature for being attracted to and held at a control magnet. In a shooting preparation state, a charge lever brings the armature of the drive unit into contact with a yoke attracting surface of the control magnet, whereby the front blade is held in a position for closing the shutter opening. Further, the rear blade is also connected to a drive unit similar to the drive unit connected to the front blade. In the shooting preparation state, a charge lever brings an armature of the drive unit into contact with a yoke attracting surface of a control magnet, whereby the rear blade is held in a position for opening the shutter opening.
Then, in shooting, the charge levers retract from respective positions for holding the front and rear blades, and the front and rear blades are held at respective traveling start positions by respective magnetic forces of the energized control magnets. Thereafter, starting with the front blade, the control magnet associated therewith is deenergized, whereby the front blade travels to the position for opening the shutter opening. A predetermined time period later, the control magnet associated with the rear blade is deenergized, whereby the rear blade travels to the position for closing the shutter opening. Thus an exposure operation is performed. After completion of traveling of the front and rear blades, the front and rear blades are moved by the associated charge levers to the respective shooting preparation positions and wait for the next shooting.
Further, single-lens reflex type digital cameras include one which performs an image pickup operation by a shutter device using a focal plane shutter and an electronic shutter in combination. In this shutter device, a rear curtain is formed by a mechanical shutter, and the electronic shutter performs resetting scanning of pixels of an image pickup device before the rear curtain travels. Electric charge accumulation start scanning by the image pickup device has a scanning pattern adapted to the traveling characteristics of the mechanical shutter as the rear curtain.
By the way, in a shutter device which controls exposure time by changing timing in which the control magnet is deenergized, if foreign matter, such as dust, water drops, or oil, adheres to the attracting surface of the armature to the yoke of the control magnet, this causes a deviation in traveling timing of the blades, which prevents normal exposure time from being obtained.
To cope with this, in order to take off foreign matter from the attracting surface of the armature to the yoke of the control magnet during or after assembling the shutter device, the attracting surface is exposed outside. Further, there has been disclosed a technique in which to prevent foreign matter from entering the attracting surface, before the shutter device is assembled to a camera, a recess is formed in a shutter base plate, for fitting a drive lever therein, and the shutter device is assembled to the camera in a state in which the yoke and the armature are attracted to the shutter base plate (see Japanese Patent Laid-Open Publication No. H09-179164).
However, the above-described conventional technique has a problem that foreign matter, such as sliding dust, or oil, enters the shutter device from movable portions of a mirror, gears, etc. after the shutter device has been assembled to the camera, and adheres to the attracting surface of the armature to the yoke.
To prevent this problem, there has been disclosed a construction that prevents foreign matter from entering the shutter device by covering the surrounding of a shutter plate, a cover plate, and a drive magnetic pole portion with a shield member (see Japanese Patent Laid-Open Publication No. 2005-227359).
However, in the conventional technique disclosed in Japanese Patent Laid-Open Publication No. 2005-227359, it is necessary to additionally provide a shield member for covering the whole shutter device, which increases the costs and degrades the ease of assembly of the camera.